Impressions using impression compositions especially in the field of dentistry often require the use of so-called individually formed impression trays. Individual impression trays are individually manufactured moldings in the form of an impression tray, which are manufactured, for example, from self-curing mixtures of methyl methacrylate/polymethyl methacrylate or from photo-curable composite plates (consisting of multifunctional photo-curable (meth-)acrylate mixtures to which glass powder has been added), in dental applications called “photo-curable individual impression tray plates.”
Silicones are usually used as impression compositions in the field of dentistry. The bond between the impression trays and silicones poses a problem, however: silicones do not by themselves adhere to plastics or composites. Nonetheless, in order to provide adhesion between silicone impression compositions and impression trays, attempts were firstly made to anchor the impression compositions stably in the impression tray, and to prevent them from lifting out of the impression tray after the impression has been taken, with the aid of mechanical retaining means, such as holes, undercuts, bent-round rims, etc., that is to say by purely mechanical means.
Attempts were also made to improve the adhesion of the silicone compositions to impression trays by molecular/mechanical means with the aid of solutions of viscous silicone polymers. Generally such silicone impression tray adhesives are solutions of only partially crosslinked silicones in volatile solvents. Since no direct chemical bonding occurs between the silicone impression composition and the partially crosslinked silicone polymers of the impression tray adhesive, those adhesives can be used both for silicone impression compositions that are crosslinked by condensation and for those crosslinked by addition.
Both above-mentioned measures for better adhesion of the silicone impression compositions to the impression trays, however, provide unsatisfactory solutions: it is especially difficult to introduce mechanical retaining means into individually manufactured impression trays since they must be produced, for example, subsequently by boring. In the case of such rigid trays, boring also easily results in stress cracks; in addition, too many mechanical retaining holes weaken the impression trays' breaking strength and resistance to bending.
The commercially available solvent-containing viscous adhesives have only an auxiliary adhesive action: in the case of relatively strong tensile forces on removal of the impression from the object of which the impression is to be taken, such as a tooth, the silicone impression lifts up from the impression tray and becomes deformed and the viscous adhesive comes away with many drawn-out threads being formed. The deformation of the impression easily results in defective fittings.
It has been known for a short time that adhesives that are used to bind non-hardening silicone re-lining materials securely to plastics for prostheses (e.g. accompanying Patent Application DE 199 05 224.7, Patent Application DE 196 35 696 A1 or Patent Specification EP 0 632 063 A1) also adhere excellently to impression trays that are slightly partially soluble. Partially soluble trays are, for example, trays made of polystyrene, polycarbonate, on monomer/polymer-based individual impression trays, such as, for example, those made of methyl methacrylate/polymethyl methacrylate, such adhesives can result in good adhesion of the silicone impression composition to precisely that type of individual impression trays.
It is problematic, however, to produce good adhesion of silicones to the surface of crosslinked methacrylates, especially to individual photo-curable impression trays based on a methacrylate composite, which are used in large numbers. The mentioned new adhesion primers for silicones fail on those types of polymerized kits.